max_execution_time

Overview

max_execution_time applies only to setting the execution timeout for read-only SELECT statements (in milliseconds).

Considerations

The max_execution_time variable takes effect only in the following scenarios:

• The cluster version meets the requirements: The minimum version of the cluster is V4.4.2 BP1 or later.
• The value of the MAX_EXECUTION_TIME parameter is greater than 0 (that is, this feature is enabled).
• The currently executing SQL statement is a single, read-only SELECT statement.

Scenarios where the max_execution_time variable does not take effect and is controlled by the ob_query_timeout variable:

• The minimum cluster version is earlier than V4.4.2 BP1.
• The MAX_EXECUTION_TIME parameter is set to 0.
• Not for SELECT statements.
• The statement is a multi-statement transaction, and the timestamp of ob_query_timeout is earlier than that of max_execution_time.
• A SELECT statement that is not read-only. For example, if a SELECT statement contains a UDF and the UDF defines DML, the timeout period for this SELECT statement is controlled by ob_query_timeout.

Privilege requirements

• Query variables

  • Global level

    The sys tenant and all user tenants can use the SHOW VARIABLES statement, or the SYS.TENANT_VIRTUAL_GLOBAL_VARIABLE view (in Oracle-compatible mode) and the information_schema.GLOBAL_VARIABLES view (in MySQL-compatible mode), to view the values of global system variables.

  • Session level

    The SHOW VARIABLES statement, or the SYS.TENANT_VIRTUAL_SESSION_VARIABLE view (in Oracle-compatible mode) and the information_schema.SESSION_VARIABLES view (in MySQL-compatible mode), can be used by the sys tenant and all user tenants to view the values of session system variables.

• Modify variables

  • The sys tenant can directly modify the values of global system variables.

  • MySQL user tenants must have the SUPER or ALTER SYSTEM privilege to modify the values of global system variables.

  • Oracle user tenants must have the ALTER SYSTEM privilege to modify the values of global system variables.

Attributes

Configuration example

Set the execution timeout for the SELECT statement to 2 milliseconds.

obclient> SET GLOBAL max_execution_time=2;

References